Text mining has been known which processes statistical analysis after dividing an uncustomary natural text through natural language processing technique and analyzes tendencies or characteristics of the text.
By using such text mining technique, useful information is extracted from mass stored document information and it is expected to be utilized effectively in business methods such as marketing and so on.
For example, methods of analyzing questionnaire reply documents by text mining are disclosed in patent document 1 and patent document 2.
With such text mining, document analysis of extracting unique words that appear frequently across a number of questionnaire reply document data or extracting related words that appear with high correlativity toward a particular word, becomes available and is utilized in marketing and so on.    [Patent Document 1] Japanese Unexamined Patent Application Publication 2001-266060    [Patent Document 2] Japanese Unexamined Patent Application Publication 2006-286026